Block copolymers can be obtained by anionic copolymerization of a conjugated diene and a monoalkenylaromatic hydrocarbon by using an organic alkali metal initiator. These types of block copolymers are diversified in characteristics, ranging from rubber-like characteristics to resin-like characteristics, depending on the content of monoalkenylaromatic compound.
When the content of monoalkenylaromatic compound is small, the produced block copolymer is a so-called thermoplastic rubber. It is a very useful polymer which shows elasticity in the unvulcanized state and is applicable for various uses such as mouldings of shoe sole, impact modifier for polystyrene resins, adhesives and binders.
The block copolymers with a high content of monoalkenylaromatic compound, such as more than 70% by weight, provide a resin possessing both excellent impact resistance and transparency, and such resins are widely used for packaging.
The elastomeric properties of block copolymers also appear to be due in part to their degree of branching. While the polymers of monoalkenylaromatic hydrocarbons have a basic straight carbon chain backbone, those with elastomeric properties always have pending alkyl radicals. For example, ethylene-propylene rubber has a structure of pending methyl radicals which appears to provide elasticity and other elastomeric properties, such as high elongation and high tensile strength.
Block copolymers have been produced, see U.S. patent specification Re 27,145 which comprise primarily those having the general structure A-B-A wherein the two terminal polymer blocks A comprise thermoplastic polymer blocks of vinylarenes, such as polystyrene, while block B is a polymer block of a selectively hydrogenated conjugated diene. The proportion of the thermoplastic terminal blocks to the center elastomeric polymer block and the relative molecular weights of each of these blocks is balanced to obtain a rubber having an optimum combination of properties such that it behaves as a vulcanized rubber without requiring the actual step of vulcanization. Moreover, these block copolymers can be designed not only with this important advantage but also so as to be handled in thermoplastic forming equipment and are soluble in a variety of relatively low cost solvents.
The selective hydrogenation has rendered the block copolymers less sensitive to oxidation and may be effected selectively as disclosed in U.S. patent specification Re 27,145. These polymers are hydrogenated block copolymers having a configuration, prior to hydrogenation of A-B-A wherein each of the A blocks is an alkenyl-substituted aromatic hydrocarbon polymer block and B is a butadiene polymer block wherein 35-55 mol per cent of the condensed butadiene units in the butadiene polymer block have 1,2-configuration.
These selectively hydrogenated ABA block copolymers are deficient in many applications in which adhesion is required due to its hydrocarbon nature. Examples include the toughening and compatibilization of polar polymers such as the engineering thermoplastics, the adhesion to high energy substrates of hydrogenated block copolymer elastomer based adhesives, sealants and coatings and the use of hydrogenated elastomer in reinforced polymer systems. However, the placement onto the block copolymer of functional groups which can provide interactions not possible with hydrocarbon polymers solves the adhesion problem and extends the range of applicability of this material.
Beyond the very dramatic improvement in interface adhesion in polymer blends, a functionalized S-EB-S component can also contribute substantially to the external adhesion characteristics often needed in polymer systems. "EB" refers to the selectively hydrogenated butadiene block which is referred to as "ethylene-butylene". These include adhesion to fibers and fillers which reinforce the polymer system; adhesion to substrates in adhesives, sealants, and coatings based on functionalized S-EB-S polymers, adhesion of decorations such as printing inks, paints, primers, and metals of systems based on S-EB-S polymers; participation in chemical reactions such as binding proteins such as heparin for blood compatibility; surfactants in polar-non-polar aqueous or non-aqueous dispersions.
Functionalized S-EB-S polymer can be described as basically commercially produced S-EB-S polymers which are produced by hydrogenation of styrene-butadiene-styrene (S-B-S) block copolymer to which is chemically attached to either the styrene or the ethylenebutylene block, chemically functional moieties.
Functionalized, selectively hydrogenated block copolymers of the type described hereinbefore have now been found which, compared with the corresponding non-functionalized selectively hydrogenated block copolymers have a higher tensile strength and a higher elongation at break, both in particular at elevated temperature; moreover, they show the improvements described hereinbefore with respect to the known functionalized, selectively hydrogenated block copolymers.